It is standard sized housing for 2.5″OD x 10″ height filters. EXTRA LARGE HOUSING allows for greater cartridge capacity, reducing the number of vessels required for high flow-rate applications Pre-Filtration System for Well and City Water The rubber O-ring provides the water tight seal between the cap and the sump. it is important that the O-ring be properly SEATED IN THE GROOVE of a water leak could occur. Whole House Water Filtration System – 1/2″ NPT Plastic Port SLIM DESIGN REDUCES SPACE REQUIRED for installation without sacrificing capacity. 1/2″ NPT INLET AND OUTLET PORT on high-flow polypropylene (HFPP) cap.